Water base adhesion promotor for polypropylene and method for coating to polypropylene materials using the promotor

ABSTRACT

The water base adhesion promotor for polypropylene comprises: 
     a grafted polypropylene chloride, which includes a polypropylene chloride moiety and a maleic anhydride moiety as bonded thereto, and which has a chlorine content of 15˜25 weight % and a maleic anhydride moiety content of 1˜5 weight %; 
     an amine-neutralized water-soluble resin; 
     a wettability-improving agent; and 
     water; and is characterized by having: 
     a combination ratio of 25˜90 weight % as of the grafted polypropylene chloride to the total of the grafted polypropylene chloride and the amine-neutralized water-soluble resin; 
     a combination ratio of 2.5˜6.0 weight % as of the wettability-improving agent to the entirety of the promotor; and 
     a solid content of 2˜10 weight % of the entirety of the promotor. 
     The method for coating to polypropylene materials comprises: 
     a pretreatment step in which a polypropylene material is beforehand washed, and then immersed into the above water base adhesion promotor, and then dried; and 
     a coating step in which a paint is coated to the material after the pretreatment step.

This application is a continuation of U.S. patent application Ser. No. 09/248,235 filed on Feb. 10, 1999 now U.S. Pat. No. 6,262,160 and claims the benefit thereof under 35 U.S.C. §120.

TECHNICAL FIELD

The present invention relates to: a water base adhesion promotor for improving the paint adhesion to polypropylene materials; and a method for coating to polypropylene materials using the promotor.

BACKGROUND ART

Polyolefins such as polypropylene are comparatively cheap and has excellent properties such as formability and chemical resistance, so they are widely used in the industrial fields including the automobile industry. The amount thereof as used tends to increase, because their recycling is possible and because their prices are low. Polypropylene materials are, for example, used for exterior decoration parts of automobiles, such as bumpers and molds, and their surfaces are usually coated to both improve their weather resistance and give the design property thereto.

The polypropylene material is inferior in wettability. Therefore, when being coated with a paint, the polypropylene material undergoes the following treatments: first, a degreasing treatment with a water, base cleaning agent and a pretreatment to enhance the wettability using a surface-active agent, and then coating and baking treatments of a primer, and then a coating treatment of a paint. Incidentally, the coating treatment of the primer is carried out to enhance the adhesion of paints, but, in fact, as much as about 70% of the amount of the primer as used is blown off and therefore is not effectively used, thus resulting in high coating cost. Furthermore, there are problems in that: the primer needs to be baked after being coated, so a large baking furnace is needed and the equipment cost is therefore high.

From the above circumstances, it is desired to develop a method for coating to polypropylene materials without coating the primer.

DISCLOSURE OF THE INVENTION Object of the Invention

An object of the present invention is to provide: a water base adhesion promotor to enhance the paint adhesion to polypropylene materials instead of the primer coating; and a method for coating to polypropylene materials using the promotor.

SUMMARY OF THE INVENTION

The present inventors made various examinations and experiments to solve the above problems. As a result, they attained the present invention by finding that: a composition, comprising a grafted polypropylene chloride of high adhesion to polypropylene materials, an amine-neutralized water-soluble resin of high water resistance, and a wettability-improving agent, could enhance the paint adhesion to polypropylene materials, so that the primer coating could be omitted.

That is to say, a water base adhesion promotor for polypropylene, according to the present invention, comprises: a grafted polypropylene chloride, which includes a polypropylene chloride moiety and a maleic anhydride moiety as bonded thereto, and which has a chlorine content of 15˜25 weight % and a maleic anhydride moiety content of 1˜5 weight %;

an amine-neutralized water-soluble resin;

a wettability-improving agent; and

water; and is characterized by having:

a combination ratio of 25˜90 weight % as of the grafted polypropylene chloride to the total of the grafted polypropylene chloride and the amine-neutralized water-soluble resin;

a combination ratio of 2.5˜6.0 weight % as of the wettability-improving agent to the entirety of the promotor; and

a solid content of 2˜10 weight % of the entirety of the promotor.

A method for coating to polypropylene materials, according to the present invention, comprises:

a pretreatment step in which a polypropylene material is beforehand washed, and then immersed into the above water base adhesion promotor, and then dried; and

a coating step in which a paint is coated to the material after the pretreatment step.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, each component, constituting the present invention water base adhesion promotor for polypropylene, is explained in detail, and then the water base adhesion promotor for polypropylene and the method for coating to polypropylene materials are explained.

(Grafted Polypropylene Chloride):

The grafted polypropylene chloride, as used in the present invention, is a component to enhance the adhesion to polypropylene materials. The grafted polypropylene chloride is a polypropylene derivative which includes a polypropylene chloride moiety and a maleic anhydride moiety as bonded thereto, and is usually used in the form of an emulsion having the high handling property.

The polypropylene chloride moiety is a moiety comprising a polypropylene having at least one chlorine atom as a substituent. In addition, the maleic anhydride moiety is a moiety as obtained by grafting maleic anhydride, and has a cyclic acid anhydride group (deriving from maleic anhydride) and/or two free carboxyl groups.

The grafted polypropylene chloride is a product by reacting a polypropylene upon maleic anhydride and chlorine to internally graft the polypropylene, and is, for example, produced by reacting chlorine and maleic anhydride upon a polypropylene. Incidentally, whichever of chlorine and maleic anhydride may be reacted earlier than the other. The reaction with chlorine is, for example, carried out by introducing a chlorine gas into a solution including a polypropylene. In addition, the reaction with maleic anhydride is, for example, carried out by reacting maleic anhydride upon a polypropylene (or its chloride) in the presence of a peroxide.

The chlorine content in the grafted polypropylene chloride is in the range of 15˜25 weight %, preferably 18˜22 weight %. In the case where the chlorine content is less than 15 weight %, the melting point of the grafted polypropylene chloride is so high that the crystallization easily occurs and that the emulsification is difficult, thus resulting in depression of the storage stability of the resultant water base adhesion promotor. On the other hand, in the case where the chlorine content exceeds 25 weight %, the grafted polypropylene chloride is noncrystalline, thus resulting in depression of the adhesion and the water resistance.

The maleic anhydride moiety content in the grafted polypropylene chloride is in the range of 1˜5 weight %, preferably 3˜4.5 weight %. In the case where the maleic anhydride moiety content is less than 1 weight %, the emulsification is difficult, thus resulting in depression of the storage stability of the resultant water base adhesion promotor. On the other hand, in the case where the maleic anhydride moiety content exceeds 5 weight %, the acid anhydride group content is too much, thus resulting in depression of the adhesion and the water resistance.

The weight-average molecular weight of the grafted polypropylene chloride is not especially limited, but is preferably in the range of 20,000˜100,000, more preferably 30,000˜80,000. In the case where the weight-average molecular weight is less than 20,000, the promotor might swell with a solvent for a top paint, so that the adhesion might be deteriorated. On the other hand, the weight-average molecular weight exceeds 100,000, the viscosity of the resultant water base adhesion promotor might be so high that the emulsification might be difficult and that the storage stability might be low.

(Amine-neutralized Water-soluble Resin):

The amine-neutralized water-soluble resin, as used in the present invention, is a resin as water-solubilized by neutralization with an amine, and is a film-formable component having high water resistance. Incidentally, for example, water-soluble resins, which are not obtained by the amine neutralization, such as polyethylene glycol and polyvinylpyrrolidone, merely have low water resistance, because, even after film formation by drying, such water-soluble resins remain and retain its water solubility. In comparison, the amine-neutralized water-soluble resin, as used in the present invention, displays high water resistance, because it volatilizes the amine in the drying step, and thus loses the water solubility.

The amine-neutralized water-soluble resin, as used in the present invention, is not especially limited if it is a resin as neutralized with an amine, and examples thereof include products by neutralization of resins such as urethane resins, alkyd resins, and acrylic resins. These may be used either alone respectively or in combinations with each other.

Examples of the amine, as used for the above neutralization, include ammonia, triethylamine, and monoethanolamine. These may be used either alone respectively or in combinations with each other.

(Wettability-improving Agent):

The wettability-improving agent, as used in the present invention, is a component to enhance the wettability of the water base adhesion promotor upon polypropylene materials (having much water-repellency). The use of this wettability-improving agent enables a coating film, resultant from the grafted polypropylene chloride and the amine-neutralized water-soluble resin as above, to adhere well to polypropylene materials.

The wettability-improving agent is not especially limited, but examples thereof include ethylene glycol hexyl ether, dimethylpolysiloxane-polyethylene glycol block polymers (Polyflow KL-245). These may be used either alone respectively or in combinations with each other. Particularly, ethylene glycol hexyl ether improves the wettability, and further does not lower the water resistance because it volatilizes in the drying step and therefore does not remain in the resultant coating film. In comparison, materials as conventionally used to enhance the wettability, such as alkylphenylpolyethylene glycol, do not volatilize in the drying step, but remain in the coating film, thus depressing the water resistance.

(Other Components):

The water base adhesion promotor of the present invention may further comprise the following other components: resin emulsions such as acrylic emulsions, urethane emulsions, and polyvinyl chloride emulsions; inorganic pigments such as titanium white and carbon black, extenders such as talc and precipitated barium; and various organic color pigments.

(Water Base Adhesion Promotor for Polypropylene and Method for Coating):

The water base adhesion promotor for polypropylene, according to the present invention, needs to comprise the grafted polypropylene chloride, the amine-neutralized water-soluble resin, the wettability-improving agent, and water (these components are explained in detail above), and may further comprise the above other components if necessary. Conditions, such as order, for mixing these components are not especially limited.

The combination ratio of the grafted polypropylene chloride, as contained in the present invention water base adhesion promotor for polypropylene, is in the range of 25˜90 weight %, preferably 30˜50 weight %, of the total (the total solid content) of the grafted polypropylene chloride and the amine-neutralized water-soluble resin. In the, case where the combination ratio of the grafted polypropylene chloride is less than 25 weight %, the adhesion and the water resistance are both low. On the other hand, in the case where the combination ratio of the grafted polypropylene chloride exceeds 90 weight %, the adhesion and the water resistance as well as the film formability are low.

The combination ratio of the wettability-improving agent is in the range of 2.5˜6.0 weight %, preferably 3.0˜4.0 weight %, of the entirety of the water base adhesion promotor. In the case where the combination ratio of the wettability-improving agent is less than 2.5 weight %, the polypropylene material crawls with the water base adhesion promotor, so uniform coating is impossible. On the other hand, in the case where the combination ratio of the wettability-improving agent exceeds 6.0 weight %, the storage stability of the water base adhesion promotor is low, and the grafted polypropylene chloride aggregates to precipitate.

The solid content of the present invention water base adhesion promotor for polypropylene is the nonvolatile matter and is in the range of 2˜10 weight %, preferably 4˜6 weight %, of the entirety of the water base adhesion promotor. In the case where the solid content is less than 2 weight %, the film thickness of the coating film resultant from the water base adhesion promotor is too thin, so the adhesion and the water resistance are both low. On the other hand, in the case where the solid content exceeds 10 weight %, marks of sagging are left after coating the water base adhesion promotor, so the resultant coating film has unevenness, and the appearance is therefore unfavorable.

The method for coating to polypropylene materials, according to the present invention, comprises the pretreatment step and the top coating step.

The pretreatment step includes the steps of immersing a washed polypropylene material into the above water base adhesion promotor and then drying the material.

The washed polypropylene material is, for example, prepared by the following steps (1)˜(3) in the pretreatment step.

(1) A step of spray-washing a polypropylene material with warm water of 60˜80° C.

(2) A step of degreasing the polypropylene material with an alkaline cleaning agent after the above step (1).

(3) A step of washing the alkaline cleaning agent off the polypropylene material by spray-washing the polypropylene material with deionized water after the above step (2).

The coating film of the water base adhesion promotor is formed on the surface of the polypropylene material by immersing the resultant washed polypropylene material into the water base adhesion promotor and then drying the material. The coating of the water base adhesion promotor can be, for example, carried out by spray coating, which is, however, economically disadvantageous. It is preferable to leave the polypropylene material fitly standing upright after the immersion and to then dry the material. The method for the above drying is not especially limited, and the drying is usually carried out with ovens such as hot-air drying ovens, far-infrared ovens, and near-infrared ovens at 60˜120° C. for 5˜15 minutes. The thickness of the dried film, as obtained from the water base adhesion promotor in the above way, is preferably in the range of 0.1˜1 μm.

The coating step includes the step of coating a top paint to the above material after the pretreatment step and is carried out by coating the top paint and then drying it.

The type of the top paint is not especially limited, but examples thereof include one-liquid melamine baking paints, two-liquid urethane paints, and one-liquid lacquer paints.

The method of coating the top paint is not especially limited, but the spray coating is preferable. The method for drying the coated top paint is not especially limited, and the drying is usually carried out with ovens such as hot-air drying ovens, far-infrared ovens, and near-infrared ovens at 70˜120° C. for 20˜60 minutes. The thickness of the dried film, as obtained from the top paint in the above way, is not especially limited, but is preferably in the range of 15˜60 μm.

In the method for coating to polypropylene materials, the use of the above water base adhesion promotor in the pretreatment step enables the omission of the primer coating. Therefore, the productivity in the coating step is largely improved.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention is more specifically illustrated by the following examples of some preferred embodiments in comparison with comparative examples not according to the invention. However, the invention is not limited to the below-mentioned examples. Hereinafter, the unit “part(s)” is “weight part(s).”

EXAMPLE 1

First, 6 parts (nonvolatile matter: 1.8 parts) of a grafted polypropylene chloride emulsion (chlorine content=16 weight %, maleic anhydride moiety content=1.5 weight %, nonvolatile matter=30 weight %), 12 parts (nonvolatile matter: 4.2 parts) of a water-soluble urethane (made by Sanyo Kasei Co., Ltd., U-Coat UWS-145, nonvolatile matter=35 weight %) (as the amine-neutralized water-soluble resin), 3 parts of ethylene glycol hexyl ether (as the wettability-improving agent), and 79 parts of water were mixed in this order under stirring, thus preparing water base adhesion promotor (1) of 100 parts in entirety. Incidentally, the ratio of (grafted polypropylene chloride)/(amine-neutralized water-soluble resin) (ratio in terms of solid content) was 30/70, and the combination ratio of ethylene glycol hexyl ether was 3 weight % of the entirety of water base adhesion promotor (1), and the solid content of water base adhesion promotor (1) was 6 weight % as determined from its nonvolatile matter.

A polypropylene material was spray-washed with warm water of 60˜80° C., and then degreased by spray-washing with an alkaline cleaning agent (Surf Cleaner PL-1000, made by Nippon Paint Co., Ltd.), and then spray-washed with deionized water of room temperature to wash the alkaline cleaning agent off, thus preparing a washed polypropylene material. This polypropylene material was immersed into water base adhesion promotor (1), and then left standing upright at room temperature for 1 minute, and then dried at 80° C. for 10 minutes. Next, an isocyanate curing type polyester resin paint (R-763, made by Morton Nippon Coatings Co., Ltd.) (as the top paint) was spray-coated to the above polypropylene material, and the coated paint was then dried at 80° C. for 40 minutes, thus obtaining coated product (1). Incidentally, the dried-film thickness was in the range of 15˜25 μm.

The properties of water base adhesion promotor (1) were evaluated by the following methods. The results thereof are shown in Table 1.

(Evaluation Method):

1. Adhesion:

A cross-cut test was carried out for the coated product in accordance with JIS K5400. First, 100 cross-cuts of 2 mm×2 mm were prepared to carry out the cellophane tape peeling-off test, and the evaluation was made on the following evaluation standard:

∘: no peeling-off was seen;

x: one or more cross-cuts peeled off.

2. Water Resistance:

The coated product was immersed into warm water of 80° C. for 3 hours, and water on the surface was then wiped off. Thereafter, the coated product was left for 1 hour, and the above adhesion evaluation was then carried out. The evaluation standard was the same as that for the adhesion.

3. Appearance:

A polypropylene material of 7.5 cm×10 cm was prepared, and then treated with the water base adhesion promotor, and then stood upright, and then dried at 80° C. for 30 minutes, thus evaluating whether a sagging mark was seen or not with the eye on the following evaluation standard:

∘: no sagging mark;

x: a sagging mark was seen.

4. Storage Stability:

A polypropylene material was immersed into the water base adhesion promotor as had been stored at room temperature for 1 month, thus evaluating whether an aggregate was seen or not with the eye on the following evaluation standard:

∘: no aggregate;

x: an aggregate was seen.

EXAMPLES 2˜4 AND COMPARATIVE EXAMPLES 1˜7

Water base adhesion promoters (2)˜(4) and comparative water base adhesion promoters (1)˜(7) were prepared to evaluate their properties in the same way as of Example 1 except that the type and the combination amount of the grafted polypropylene chloride emulsion and the combination amounts of the water-soluble urethane and the ethylene glycol hexyl ether were changed to those as shown in Tables 1 and 2. Tables 1 and 2 further show the ratio of (grafted polypropylene chloride)/(amine-neutralized water-soluble resin) (ratio in terms of solid content) and the combination ratio and the solid content of the ethylene glycol hexyl ether.

TABLE 1 Example 1 2 3 4 Water base Grafted 1.8 1.5 4.0 4.0 adhesion polypropylene promotor chloride (CPO) (parts)*1 Water-soluble 4.2 1.5 6.0 1.0 urethane (AU) Ethylene glycol 3.0 5.0 3.0 4.0 hexyl ether (EGHE) Chlorine content of CPO 16 21 25 21 (weight %) Maleic anhydride content of 1.5 4.5 1.0 4.5 CPO (weight %) CPO/AU (ratio in terms of 30/70 50/50 40/60 80/20 solid content) Combination ratio of EGHE 3 5  3 4 (weight %) Solid content (weight %) 6 3 10 5 Evaluation Adhesion ◯ ◯ ◯ ◯ results Water resistance ◯ ◯ ◯ ◯ Appearance ◯ ◯ ◯ ◯ Storage stability ◯ ◯ ◯ ◯ *1 Amount of each component in 100 weight parts of water base adhesion promotor; the balance is water.

TABLE 2 Comparative Example 1 2 3 4 5 6 7 Water Grafted 1.0 9.5 1.8 1.8 1.8 0.5 6.0 based poly- adhesion propylene promoter chloride (parts)*1 (CPO) Water- 4.0 0.5 4.2 4.2 4.2 0.5 1.0 soluble urethane (AU) Ethylene 3.0 3.0 3.0 3.0 7.0 3.0 3.0 glycol hexyl ether (EGHE) Chlorine content of 21 16 27 21 21 21 21 CPO (weight %) Maleic anhydride 4.5 1.5 1.5 7.0 4.5 4.5 4.5 content of CPO (weight %) CPO/AU (ratio in 20/80 95/5 30/70 30/70 30/70 50/50 50/50 terms of solid content) Combination ratio 3 3 3 3 7 3 3 of EGHE (weight %) Solid content 5 10 6 6 6 1 12 (weight %) Evalua- Adhesion x x x x ∘ x ∘ tion Water x x x x ∘ x ∘ re- resistance sults Appear- ∘ ∘ ∘ ∘ ∘ ∘ x ance Storage — — — — x — — stability *1 Amount of each component in 100 weight parts of water base adhesion promotor; the balance is water.

<Evaluation results>:

Examples 1˜4 all provide excellent results with regard to the adhesion, the water resistance, the appearance, and the storage stability, and enable the omission of the conventional primer coating step. Comparative Examples 1 and 2 provide inferior results with regard to the adhesion and the water resistance, because the combination ratio of the grafted polypropylene chloride is out of the claimed range. Comparative Example 3 provides inferior results with regard to the adhesion and the water resistance, because the chlorine content of the grafted polypropylene chloride is too large. Comparative Example 4 provides inferior results with regard to the adhesion and the water resistance, because the maleic acid moiety content is too large. Comparative Example 5 provides inferior results with regard to the storage stability, because the combination ratio of the ethylene glycol hexyl ether is too large. Comparative Example 6 provides inferior results with regard to the adhesion and the water resistance, because the coating film resultant from the water base adhesion promotor is thin due to too small solid content. Comparative Example 7 provides inferior results with regard to the appearance, because the coating film resultant from the water base adhesion promotor is thick due to too large solid content.

INDUSTRIAL APPLICATION

The use of the present invention water base adhesion promotor for polypropylene in the pretreatment step prior to coating of polypropylene materials enables the omission of the primer coating, and further, provides excellent results with regard to the adhesion of the paint and the water resistance and appearance of the coating film.

The present invention method for coating to polypropylene materials involves the use of the above water base adhesion promotor in the pretreatment step and therefore enables the omission of the primer coating and the great improvement of the productivity of the coating step. In addition, in this method, because the polypropylene materials can be coated by immersion into the water base adhesion promotor, there is no loss of the water base adhesion promotor, so there are economical advantages. 

What is claimed is:
 1. An adhesion promotor for polyolefin, wherein the adhesion promotor has been dried and is in a film form on the polyolefin, comprising: a) a grafted polyolefin chloride in the film; b) a wettability-improving agent in the film; c) a resin in the film, wherein: i) the resin was neutralized and was made water-soluble with an amine and was then applied in the film form on the polyolefin; ii) the amine of the amine-neutralized resin was then volatized from the amine-neutralized resin; and iii) after the amine of the amine-neutralized resin was volatized from the amine-neutralized resin, the resin lost water-solubility to provide a high water resistant resin for the film; and d) wherein a thickness of the film is in a range of 0.1 to 1 μm.
 2. An adhesion promotor for polypropylene, wherein the adhesion promotor has been dried and is in a film form on the polypropylene, comprising: a) a grafted polypropylene chloride in the film; b) a wettability-improving agent in the film; c) a resin in the film, wherein: i) the resin was neutralized and was made water-soluble with an amine and was then applied in the film form on the polypropylene; ii) the amine of the amine-neutralized resin was then volatized from the amine-neutralized resin; and iii) after the amine of the amine-neutralized resin was volatized from the amine-neutralized resin, the resin lost water-solubility to provide a high water resistant resin for the film; and d) wherein a thickness of the film is in a range of 0.1 to 1 μm. 